A Sun-powered sail pushes a robotic probe beyond the edge of the solar system in this artist's concept. Such sails could eventually reach perhaps one percent of the speed of light, which would still require centuries of travel to reach even the nearest stars. [NASA/MSFC]

In a lot of sci-fi movies and TV shows, humanity’s fate is in the stars. According to these visions, we’ll be warping off to Alpha Centauri and beyond any day now.

The reality is far more daunting. Consider that the most distant spacecraft yet launched, Voyager 1, recently exited the solar system — 35 years after it left Earth. At that rate, if the probe were headed toward Alpha Centauri — our nearest stellar neighbors — it would need another 75,000 years to get there.

Even so, a few scientists and engineers are thinking seriously about how we might reach the stars.

One leading idea is solar sails — propelling a starship with the pressure of sunlight. Such a ship might reach a few percent of the speed of light — but its sail would be as big as Alabama and the ship would need a thousand years to reach Alpha Centauri. Change the power source from sunlight to giant lasers and you could cut the travel time to a century. But such a laser would require as much power as all of humanity generates today.

There are other possibilities, but they’re even more difficult. Giant “worldships” could carry hundreds of people on a one-way trip that would last many generations. And even a faster-than-light warp drive might be possible — but wildly impractical.

For the time being, then, we’re stuck in our own solar system. Yet some small steps into the galaxy could help set the stage for journeys to other stars; more about that tomorrow.